This invention concerns a drive for a thin-film electroluminescent (EL) display panel.
At present, a line-film method is used to drive a thin-film EL display panel having a matrix structure, and the upper limit of the frame frequency is limited to some extent by the number of electrodes on the scan side. Recent increases in the display capacity of the EL display panel have been accompanied by an increase in the number of scan-side electrodes, resulting in an incumbent drop in a frame frequency.
FIG. 2 shows a basic structure of the thin-film EL display panel. In this figure, 4 is a ZnS layer which is a luminescent layer of the thin-film EL display panel; manganese and other substances are added as active material forming a luminescent center. Number 3 and 5 are the dielectric layers of Si.sub.3 N.sub.4, SiO.sub.2, Al.sub.3 O.sub.3, and other materials; 2 is the transparent electrode of indium tin oxide (I.T.O.) on a display side; 6 is the backplate of aluminum; and 1 is a glass substrate.
Though light is produced as electroluminescence when an appropriate AC pulse voltage 7 is applied to a thin-film EL display panel of such a structure, two intermittent light emissions are obtained per one cycle as shown in FIG. 3 (f: frequency). For example, a 120-Hz light emission is obtained for a 60-Hz AC pulse. The level of these two light emissions may vary by a maximum 10% due to an incomplete symmetry in the component structure of the light-emitting layer.
Human sight perceives frequencies below a certain level emitted by an intermittent illuminant as flicker. This limit is said to be 40 to 50 Hz, depending upon personal differences and light waveforms. In the case of thin-film EL display panels, since the emitted pulse will be 60 Hz given an applied AC pulse of 30 Hz, the luminescence should not be perceived as a flicker, but because the two emission levels in each cycle are not equal, the emission is perceived as a 30-Hz flicker by the human eye. This fact is a major drawback to the display quality of thin-film EL display panels.